MIP4 Working Group Rajeev Koodli Internet-Draft Charles Perkins Intended status: Experimental Nokia Research Center Expires: September 1, 2007 February 28, 2007 Mobile IPv4 Fast Handovers draft-ietf-mip4-fmipv4-05.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on September 1, 2007. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract This document adapts the Mobile IPv6 Fast Handovers to improve delay and packet loss resulting from Mobile IPv4 handover operations. Specifically, this document addresses movement detection, IP address configuration and location update latencies during a handover. For reducing the IP address configuration latency, the document proposes that the new Care-of Address is always made to be the new access router's IP address. Additional mechanisms may be defined in the future versions of this document. Koodli & Perkins Expires September 1, 2007 [Page 1] Internet-Draft MIP4 Fast Handovers February 2007 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Factors Affecting Handover . . . . . . . . . . . . . . . . . . 4 4. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.2. Operation . . . . . . . . . . . . . . . . . . . . . . . . 6 5. Using Previous FA Notification Extension . . . . . . . . . . . 9 6. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 9 6.1. Fast Binding Update (FBU) . . . . . . . . . . . . . . . . 9 6.2. Fast Binding Acknowledgment (FBAck) . . . . . . . . . . . 10 6.3. Router Solicitation for Proxy Advertisement (RtSolPr) . . 12 6.4. Proxy Router Advertisement (PrRtAdv) . . . . . . . . . . . 13 6.5. Inter-Access Router Messages . . . . . . . . . . . . . . . 16 6.5.1. Handover Initiate (HI) . . . . . . . . . . . . . . . . 16 6.5.2. Handover Acknowledge (HAck) . . . . . . . . . . . . . 17 7. Option Formats . . . . . . . . . . . . . . . . . . . . . . . . 19 7.1. Link-Layer Address Option Format . . . . . . . . . . . . . 19 7.2. New IPv4 Address Option Format . . . . . . . . . . . . . . 20 7.3. New Router Prefix Information Option . . . . . . . . . . . 21 8. Security Considerations . . . . . . . . . . . . . . . . . . . 22 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 23 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23 11.1. Normative References . . . . . . . . . . . . . . . . . . . 23 11.2. Informative References . . . . . . . . . . . . . . . . . . 24 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 24 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25 Intellectual Property and Copyright Statements . . . . . . . . . . 26 Koodli & Perkins Expires September 1, 2007 [Page 2] Internet-Draft MIP4 Fast Handovers February 2007 1. Introduction This document adapts the fast handover specification [rfc4068] to IPv4 networks. The fast handover protocol specified in this document is particularly interesting for operation over links such as IEEE 802 wireless links. Fast handovers are not typically needed for wired media due to the relatively large delays attributable to establishing new connections in today's wired networks. Mobile IPv4 [rfc3344] registration messages are re-used (with new type numbers) in this document to enable faster implementation using existing Mobile IPv4 software. This draft does not rely on link-layer triggers for protocol operation, but performance will typically be enhanced by using the appropriate triggers when they are available. This document assumes that the reader is familiar with the basic operation and terminology of Mobile IPv4 [rfc3344] and Fast Handovers for Mobile IPv6 [rfc4068]. The active agents that enable continued packet delivery to a mobile node (MN) are the access routers on the networks that the mobile node connects to. Handover means that the mobile node changes its network connection, and we consider the scenario in which this change means change in access routers. The mobile node utilizes the access routers as default routers in the normal sense, but also as partners in mobility management. Thus, when the mobile node moves to a new network, it processes handover-related signaling in order to identify and develop a relationship with a new access router. In this document, we call the previous access router PAR and the new access router NAR, consistent with the terminology in [rfc4068]. Unless otherwise mentioned, a PAR is also a Previous Foreign Agent (PFA) and a NAR is also a New Foreign Agent (NFA). On a particular network, a mobile node may obtain its IP address via DHCP [rfc2131] (i.e., Co-located Care-of Address) or use the Foreign Agent CoA. During a handover, the new CoA (NCoA) is always made to be that of NAR. This allows a mobile node to receive and send packets using its previous CoA (PCoA), so that delays resulting from IP configuration (such as DHCP address acquisition delay) subsequent to attaching to the new link are disengaged from affecting the existing sessions. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 2. Terminology The terminology used in this document in based on [rfc4068] and Koodli & Perkins Expires September 1, 2007 [Page 3] Internet-Draft MIP4 Fast Handovers February 2007 [rfc3344]. We provide some definitions below for convenience. Mobile Node (MN): A Mobile IPv6 host. Access Point (AP): A Layer 2 device connected to an IP subnet that offers wireless connectivity to an MN. An Access Point Identifier (AP-ID) refers to the AP's L2 address. Sometimes, AP-ID is also referred to as a Base Station Subsystem ID (BSSID). Access Router (AR): The MN's default router. Previous Access Router (PAR): The MN's default router prior to its handover. New Access Router (NAR): The MN's default router subsequent to its handover. Previous CoA (PCoA): The MN's Care of Address valid on PAR's subnet. New CoA (NCoA): The MN's Care of Address valid on NAR's subnet. Handover: A process of terminating existing connectivity and obtaining new IP connectivity. (AP-ID, AR-Info) tuple: Contains an access router's L2 and IP addresses, and the prefix valid on the interface to which the Access Point (identified by AP-ID) is attached. The triplet [Router's L2 address, Router's IP address, Prefix] is called "AR- Info". 3. Factors Affecting Handover Both the link-layer operations and IP layer procedures affect the perceived handover performance. However, the overall performance is also (always) a function of specific implementation of the technology as well as the system configuration. This document only specifies IP layer protocol operations. The purpose of this section is to provide an illustration of events that affect handover performance, but it is purely informative. The IP layer handover delay and packet loss are influenced by latencies due to movement detection, IP address configuration and Mobile IP registration procedure. Movement detection latency comes from the need to reliably detect movement to a new subnet. This is a function of frequency of router advertisements as well as default Koodli & Perkins Expires September 1, 2007 [Page 4] Internet-Draft MIP4 Fast Handovers February 2007 agent reachability. IP address configuration latency depends on the particular IP CoA being used. If co-located mode with DHCP is used, the latency is quite likely going to be higher and unacceptable for real-time applications such as Voice over IP. Finally, the Mobile IP registration procedure needs a round-trip of delay between the Mobile Node and its Home Agent over the Internet. This delay is incurred after the mobile node performs movement detection and IP configuration. Underlying the IP operations are link-layer procedures. These are clearly technology-specific. For instance in IEEE 802.11, the handover operation typically involves scanning access points over all available channels, selecting a suitable access point, and associating with it. It may also involve performing access control operations such as those specified in IEEE 802.1X [ieee-802.1x]. These delays contribute to the handover performance. Optimizations are being proposed for standardization in IEEE, for instance see [ieee-802.11r] and [ieee-802.21]. Together with appropriate implementation techniques, these optimizations can provide the required level of delay support at the link-layer for real-time applications. 4. Protocol 4.1. Overview The design of the protocol is the same as for Mobile IPv6 [rfc4068]. Readers should consult [rfc4068] for details, and here we provide a summary. The protocol avoids the delay due to movement detection and IP configuration and disengages Mobile IP registration delay from the time-critical path. The protocol provides the surrounding network neighborhood information so that a mobile node can determine whether it is moving to a new subnet even before the handover. The information provided and the signaling exchanged between the local mobility agents allows the mobile node to send and receive packets immediately after handover. In order to disengage the Mobile IP registration latency, the protocol provides routing support for the continued use of a mobile node's previous CoA. After a mobile node obtains its IPv4 care-of address, it builds a neighborhood access point and subnet map using the Router Solicitation for Proxy Advertisement (RtSolPr) and Proxy Router Advertisement (PrRtAdv) messages. The mobile node may scan for access points (APs) based on the configuration policy in operation for its wireless network interface. If a scan results in a new AP Koodli & Perkins Expires September 1, 2007 [Page 5] Internet-Draft MIP4 Fast Handovers February 2007 discovery, the mobile node resolves the corresponding AP Identifier to subnet information using the RtSolPr and PrRtAdv messages mentioned above. At some point, the mobile node decides to undergo handover. It sends an FBU message to PAR from the previous link or from the new link. FBU message enables creation of a binding between the mobile node's previous CoA and the new CoA. The coordination between the access routers is done by way of the Handover Initiate (HI) and Handover Acknowledge (HAck) messages defined in [rfc4068]. After these signals have been exchanged between the previous and new access routers (PAR and NAR), data arriving at PAR will be tunneled to NAR for delivery to the newly arrived mobile node. The purpose of HI is to securely deliver the routing parameters for establishing this tunnel. The tunnel is created by the access routers in response to the delivery of the FBU from the mobile node. 4.2. Operation In response to a handover trigger or indication, the mobile node sends a Fast Binding Update message to Previous Access Router (PAR) (see Section Section 6.1). Depending on the Mobile IP mode of operation, the PCoA is either the Home Address (in FA CoA mode) or co-located CoA (in CCoA mode). The FBU message SHOULD be sent when the mobile node is still connected to PAR. When sent in this "predictive" mode, the fields in the FBU are used as follows: "Home Address" field must be the PCoA (which can be either the Home Address or the co-located CoA) Home Agent field, even though redundant, must be set to PAR's IP address Care-of Address field must be the NAR's IP address discovered via PrRtAdv message Destination IP address must be PAR's IP address Source IP address must be the PCoA (which can be either the Home Address or the co-located CoA) As a result of processing the FBU, PAR creates a binding between PCoA and NAR's IP address in its routing table. The PAR sends an FBack message (see Section Section 6.2) as a response to the mobile node. Koodli & Perkins Expires September 1, 2007 [Page 6] Internet-Draft MIP4 Fast Handovers February 2007 The timeline for the predictive mode of operation (adapted from [rfc4068]) is shown in Figure Figure 1. MN PAR NAR | | | |------RtSolPr------->| | |<-----PrRtAdv--------| | | | | |------FBU----------->|--------HI--------->| | |<------HAck---------| | <--FBack---|--FBack---> | | | | disconnect forward | | packets===============>| | | | | | | connect | | | | | |--------- FBU --------------------------->| |<=================================== deliver packets | |<-----FBU-----------| Figure 1: Predictive Fast Handover The mobile node sends the FBU regardless of its previous transmission when attachment to a new link is detected. This minimally allows NAR to detect mobile node's attachment, but also the retransmission of FBU when an FBack has not been received yet. When sent in this "reactive" mode, the following fields in FBU are set differently compared to the predictive mode: Destination IP address must be NAR's IP address Source IP address must be PCoA (either the Home Address or the co- located CoA) When NAR receives FBU, it may already have processed the HI message and created a host route entry for the PCoA. In that case, NAR should immediately forward arriving and buffered packets including the FBAck message. In any case, NAR MUST forward the contents of this message, starting from the Type field, to PAR, which means the Source and Destination IP addresses in the new packet now contain the IP addresses of NAR and PAR respectively. Koodli & Perkins Expires September 1, 2007 [Page 7] Internet-Draft MIP4 Fast Handovers February 2007 The reactive mode of operation (adapted from [rfc4068]) is illustrated in Figure Figure 2. MN PAR NAR | | | |------RtSolPr------->| | |<-----PrRtAdv--------| | | | | disconnect | | | | | | | | connect | | |-----------FBU-------|------------------->| | |<-----FBU-----------| | |------FBack-------->| | forward | | packets===============>| | | | |<=================================== deliver packets | | Figure 2: Reactive Fast Handover The Handover Initiate (HI) and Handover Acknowledge (HAck) messages serve to establish a bidirectional tunnel between the routers to support packet forwarding for PCoA. The tunnel itself is established as a response to the FBU message. The PAR sends HI message with Code = 0 when it receives FBU with source IP address set to PCoA. The PAR sends HI with Code = 1 when it receives FBU with source IP address not set to PCoA (i.e., when received from NAR). This allows NAR to disambiguate HI message processing sent as a response to predictive and reactive modes of operation. If NAR receives a HI message with Code = 1, and it has already set up a host route entry and a reverse tunnel for PCoA, it should silently discard the HI message. The protocol provides an option for NAR to return NCoA for use by the mobile node. When NAR can provide an NCoA for exclusive use of the mobile node, the address is supplied in the HAck message. The PAR includes this NCoA in FBack. Exactly how NAR manages the address pool from which it supplies NCoA is not specified in this document. Nevertheless, the MN should be prepared to use this address instead of performing DHCP or similar operations to obtain an IPv4 address. Even though the mobile node can obtain this NCoA from the NAR, it is Koodli & Perkins Expires September 1, 2007 [Page 8] Internet-Draft MIP4 Fast Handovers February 2007 unaware of the address at the time it sends an FBU. Hence, it binds PCoA to NAR's IP address as before. 5. Using Previous FA Notification Extension Sending FBU from the new link (i.e., reactive mode) is similar to using the extension defined in [draft-mip4-ro]. However, with the neighborhood information gathered using the proxy router messages (see Section Section 6.3, Section Section 6.4), movement detection and router discovery delays are avoided even in the reactive case. The FBU and FBAck messages defined in this document can be naturally used even when no neighborhood information is available. 6. Message Formats 6.1. Fast Binding Update (FBU) The FBU format is bitwise identical to the Registration Request format in [rfc3344]. The same destination port number, 434, is used, but the FBU and FBAck messages in this specification have new message type numbers. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type |x|x|D|M|G|r|T|x| reserved | Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Home Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Home Agent | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Care-of Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Identification + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extensions ... +-+-+-+-+-+-+-+- Figure 3: Fast Binding Update (FBU) Message Koodli & Perkins Expires September 1, 2007 [Page 9] Internet-Draft MIP4 Fast Handovers February 2007 Source address: The interface address from which the message is sent. Either PCoA (co-located or Home Address), or NAR's IP address (when forwarded from NAR to PAR). Destination Address: The IP address of the Previous Access Router or the New Access Router. Source Port: variable Destination port: 434 Type: To be assigned by IANA Flags: See [rfc3344]. The 'S' and 'B' flags in [rfc3344] are sent as zero, and ignored on reception. reserved: Sent as zero, ignored on input Lifetime: The number of seconds remaining before binding expires. MUST NOT exceed 10 seconds. Home Address: MUST be PCoA, which can either be the co-located CoA or the Home Address Home Agent: The Previous Access Router's global IP address Care-of Address: The New Access Router's global IP address Identification: a 64-bit number used for matching an FBU with FBack. Identical to usage in [rfc3344] Extensions: MUST contain the MN - PAR Authentication Extension 6.2. Fast Binding Acknowledgment (FBAck) The FBAck format is bitwise identical to the Registration Reply format in [rfc3344]. Koodli & Perkins Expires September 1, 2007 [Page 10] Internet-Draft MIP4 Fast Handovers February 2007 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Code | reserved | Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Home Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Home Agent | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Identification + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extensions ... +-+-+-+-+-+-+-+- Figure 4: Fast Binding Acknowledgement (FBAck) Message Source address: Typically copied from the destination address of the FBU message Destination Address: Copied from the Source IP address in FBU message Source Port: variable Destination port: copied from the source port in FBU message Type: To be assigned by IANA Code: Indicates the result of processing FBU message. Code = 0 means Fast Binding Update accepted. Code = 1 means Fast Binding Update accepted but NCoA is supplied as an extension. reserved: Sent as zero, ignored on input Lifetime: The granted number of seconds remaining before binding expires. Home Address: PCoA (i.e., either co-located CoA or Home Address) Home Agent: The Previous Access Router's global IP address Koodli & Perkins Expires September 1, 2007 [Page 11] Internet-Draft MIP4 Fast Handovers February 2007 Identification: a 64-bit number used for matching FBU. Copied from the field in FBU for which this FBack is a reply. Extensions: The PAR - MN Authentication extension MUST be present. In addition, an NCoA option MUST be present when NAR supplies the NCoA. If the FBAck message indicates that the new care-of address is a Foreign Agent care-of address [rfc3344], then the mobile node MUST set the 'D' bit in its Registration Request message that it uses to register the NCoA with its home agent. 6.3. Router Solicitation for Proxy Advertisement (RtSolPr) Mobile Nodes send Router Solicitation for Proxy Advertisement in order to prompt routers for Proxy Router Advertisements. All the link-layer address options have the format defined in Section 7.1. The message format and processing rules are identical to those defined in [rfc4068]. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Code | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Subtype | Reserved | Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Options ... +-+-+-+-+-+-+-+-+-+-+-+- Figure 5: Router Solicitation for Proxy Advertisement (RtSolPr) Message IP Fields: Source Address: An IP address assigned to the sending interface Destination Address: The address of the Access Router or the all routers multicast address. Time-to-Live: At least 1. See [rfc1256]. Koodli & Perkins Expires September 1, 2007 [Page 12] Internet-Draft MIP4 Fast Handovers February 2007 ICMP Fields: Type: To be assigned by IANA Code: 0 Checksum: The 16-bit one's complement of the one's complement sum of the ICMP message, start ing with the ICMP Type. For computing the checksum, the Checksum and the Reserved fields are set to 0. See [rfc1256]. Subtype: To be assigned by IANA Reserved: MUST be set to zero by the sender and ignored by the receiver. Identifier: MUST be set by the sender so that replies can be matched to this Solicitation. Valid Options: New Access Point Link-layer Address: The link-layer address or identification of the access point for which the MN requests routing advertisement information. It MUST be included in all RtSolPr messages. More than one such address or identifier can be present. This field can also be a wildcard address (see Section 7.1). 6.4. Proxy Router Advertisement (PrRtAdv) Access routers send out Proxy Router Advertisement message gratuitously if the handover is network-initiated or as a response to RtSolPr message from a mobile node, providing the link-layer address, IP address and subnet prefixes of neighboring routers. All the link- layer address options have the format defined in Section 7.1. The message format and processing rules are identical to those defined in [rfc4068]. Koodli & Perkins Expires September 1, 2007 [Page 13] Internet-Draft MIP4 Fast Handovers February 2007 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Code | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Subtype | Reserved | Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Options ... +-+-+-+-+-+-+-+-+-+-+-+- Figure 6: Proxy Router Advertisement (PrRtAdv) Message IP Fields: Source Address: An IP address assigned to the sending interface Destination Address: The Source Address of an invoking Router Solicitation for Proxy Advertisement or the address of the node the Access Router is instructing to handover. Time-to-Live At least 1. See [rfc1256]. ICMP Fields: Type: To be assigned by IANA Code 0, 1, 2, 3 or 4. See below. Checksum: The 16-bit one's complement of the one's complement sum of the ICMP message, start- ing with the ICMP Type. For computing the checksum, the Checksum and the Reserved fields are set to 0. See [rfc1256]. Subtype: To be assigned by IANA. Reserved: MUST be set to zero by the sender and ignored by the receiver. Identifier: Copied from Router Solicitation for Proxy Advertisement or set to Zero if unsolicited. Valid Options in the following order: New Access Point Link-layer Address: The link-layer address or identification of the access point is copied from RtSolPr message. This option MUST be present. Koodli & Perkins Expires September 1, 2007 [Page 14] Internet-Draft MIP4 Fast Handovers February 2007 New Router's Link-layer Address: The link-layer address of the Access Router for which this message is proxied for. This option MUST be included when Code is 0 or 1. New Router's IP Address: The IP address of NAR. This option MUST be included when Code is 0 or 1. New Router Prefix Information Option: The number of leading bits that define the network number of the corresponding Router's IP Address option (see above). New CoA Option: MAY be present when PrRtAdv is sent unsolicited. PAR MAY compute new CoA using NAR's prefix information and the MN's L2 address, or by any other means. In any case, the MN should be prepared to use this address instead of performing DHCP or similar operations to obtain an IPv4 address. A PrRtAdv with Code 0 means that the MN should use the [AP-ID, AR- Info] tuple present in the options above. In this case, the Option- Code field (see Section 7.1) in the New AP LLA option is 1, reflecting the LLA of the access point for which the rest of the options are related, and the Option-Code for the New Router's LLA option is 3. Multiple tuples may be present. A PrRtAdv with Code 1 means that the message is sent unsolicited. If a New IPv4 option (see Figure 10) is present following the New Router Prefix Information option (see Section 7.3), the MN SHOULD use the supplied NCoA and send the FBU immediately or else stand to lose service. This message acts as a network-initiated handover trigger. The Option-Code field (see Section 7.1) in the New AP LLA option in this case is 1 reflecting the LLA of the access point for which the rest of the options are related. A Proxy Router Advertisement with Code 2 means that no new router information is present. The LLA option contains an Option-Code value that indicates a specific reason (see Section 7.1). A Proxy Router Advertisement with Code 3 means that new router information is only present for a subset of access points requested. The Option-Code values in the LLA option distinguish different outcomes (see Section 7.1). A Proxy Router Advertisement with Code 4 means that the subnet information regarding neighboring access points is sent unsolicited, but the message is not a handover trigger, unlike when the message is Koodli & Perkins Expires September 1, 2007 [Page 15] Internet-Draft MIP4 Fast Handovers February 2007 sent with Code 1. Multiple tuples may be present. When a wildcard AP identifier is supplied in the RtSolPr message, the PrRtAdv message should include any 'n' [Access Point Identifier, Link-Layer Address option, Prefix Information Option] tuples corresponding to the PAR's neighborhood. 6.5. Inter-Access Router Messages 6.5.1. Handover Initiate (HI) The Handover Initiate (HI) is an ICMP message sent by an Access Router (typically PAR) to another Access Router (typically NAR) to initiate the process of a mobile node's handover. The message format and processing rules are identical to those defined in [rfc4068]. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Code | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Subtype |S|U| Reserved | Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Options ... +-+-+-+-+-+-+-+-+-+-+-+- Figure 7: Handover Initiate (HI) Message IP Fields: Source Address: The IP address of the PAR Destination Address: The IP address of the NAR Time-to-Live: At least 1. See [rfc1256]. ICMP Fields: Type: To be assigned by IANA Code: 0 or 1. See below Koodli & Perkins Expires September 1, 2007 [Page 16] Internet-Draft MIP4 Fast Handovers February 2007 Checksum: The 16-bit one's complement of the one's complement sum of the ICMP message, start- ing with the ICMP Type. For computing the checksum, the Checksum and the Reserved fields are set to 0. See [rfc1256]. Subtype: To be assigned by IANA S: Assigned address configuration flag. When set, this message requests a new CoA to be returned by the destination. May be set when Code = 0. MUST be 0 when Code = 1. U: Buffer flag. When set, the destination SHOULD buffer any packets towards the node indicated in the options of this message. Used when Code = 0, SHOULD be set to 0 when Code = 1. Reserved: MUST be set to zero by the sender and ignored by the receiver. Identifier: MUST be set by the sender so replies can be matched to this message. Valid Options: Link-layer address of MN: The link-layer address of the MN that is undergoing handover to the destination (i.e., NAR). This option MUST be included so that the destination can recognize the MN. Previous Care of Address: The IP address used by the MN while attached to the originating router. This option MUST be included so that a host route can be established on the NAR. New Care of Address: This option MAY be present when the MN wishes to use a new IP address when connected to the destination. When the 'S' bit is set, NAR MAY provide this address in HAck, in which case t he MN should be prepared to use this address instead of performing DHCP or similar operations to obtain an IPv4 address. 6.5.2. Handover Acknowledge (HAck) The Handover Acknowledgment message is a new ICMP message that MUST be sent (typically by NAR to PAR) as a reply to the Handover Initiate (HI) (see Section Section 6.5.1) message. The message format and processing rules are identical to those defined in [rfc4068]. Koodli & Perkins Expires September 1, 2007 [Page 17] Internet-Draft MIP4 Fast Handovers February 2007 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Code | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Subtype | Reserved | Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Options ... +-+-+-+-+-+-+-+-+-+-+-+- Figure 8: Handover Acknowledge (HAck) Message IP Fields: Source Address: Copied from the destination address of the Handover Initiate Message to which this message is a response. Destination Address: Copied from the source address of the Handover Initiate Message to which this message is a response. Time-to-Live: At least 1. See [rfc1256]. ICMP Fields: Type: To be assigned by IANA Code: 0: Handover Accepted 1: Handover Accepted, NCoA not valid 2: Handover Accepted, NCoA in use 3: Handover Accepted, NCoA assigned (used in Assigned addressing) 4: Handover Accepted, NCoA not assigned 128: Handover Not Accepted, reason unspecified 129: Administratively prohibited 130: Insufficient resources Checksum: The 16-bit one's complement of the one's complement sum of the ICMP message, start- ing with the ICMP Type. For computing the checksum, the Checksum and the Reserved fields are set to 0. See [rfc1256]. Subtype: To be assigned by IANA. Koodli & Perkins Expires September 1, 2007 [Page 18] Internet-Draft MIP4 Fast Handovers February 2007 Reserved: MUST be set to zero by the sender and ignored by the receiver. Identifier: Copied from the corresponding field in the Handover Initiate message this message is in response to. Valid Options: New Care of Address: If the 'S' flag in the HI message is set, this option MUST be used to provide NCoA the MN should use when connected to this router. This option MAY be included even when 'S' bit is not set, e.g., Code 2 above. The MN should be prepared to use this address instead of performing DHCP or similar operations to obtain an IPv4 address. The Code 0 is the expected average case of a handover being accepted and the routing support provided for the use of PCoA. The rest of the Code values pertain to the use of NCoA (which is common in [rfc4068]). Code values 1 and 2 are for cases when the MN proposes an NCoA and the NAR provides a response. Code 3 is when the NAR provides NCoA (which could be the same as that proposed by the MN). Code 4 is when the NAR does not provide NCoA, but instead provides routing support for PCoA. 7. Option Formats The options in this section are specified as extensions for the HI and HAck messages, as well as for the PrRtSol and PrRtAdv messages. 7.1. Link-Layer Address Option Format 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Option-Code | LLA ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 9: Link Layer Address Option Format Fields: Type: To be assigned by IANA Koodli & Perkins Expires September 1, 2007 [Page 19] Internet-Draft MIP4 Fast Handovers February 2007 Option-Code: 0: wildcard requesting resolution for all nearby access points 1: Link-Layer Address of the New Access Point 2: Link-Layer Address of the MN 3: Link-Layer Address of the NAR 4: Link-Layer Address of the source of the RtSolPr or PrRtAdv message 5: The access point identified by the LLA belongs to the current interface of the router 6: No prefix information available for the access point identified by the LLA 7: No fast handovers support available for the access point identified by the LLA Length: The length of the option (including the Type, Length and Option-Code fields) in units of 8 octets. Link-Layer Address: The variable length link-layer address. The content and format of this field (including byte and bit ordering) depends on the specific link-layer in use. There is no length field for the LLA itself. Implementations must determine the length of the LLA based on the specific link technology where the protocol is run. The total size of the LLA option itself must be a multiple of 8 octets. Hence, padding may be necessary depending on the size of the LLA used. In such a case, the padN option [rfc2460] MUST be used. As an example, when the LLA is 6 bytes (meaning 7 bytes of padding is necessary to bring the LLA option length to 2), the padN option will have a length field of 5 and 5 bytes of zero-valued octets (see [rfc2460]). 7.2. New IPv4 Address Option Format This option is used to provide the new router's IPv4 address or the NCoA in PrRtAdv, as well as PCoA and NCoA in HI and HAck messages. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Option-Code | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | New IPv4 Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Koodli & Perkins Expires September 1, 2007 [Page 20] Internet-Draft MIP4 Fast Handovers February 2007 Figure 10: New IPv4 Address Option Format Fields: Type: To be assigned by IANA Length: The length of the option (including the Type, Length and Option-Code fields) in units of 8 octets. Option-Code: 1: Previous CoA 2: New CoA 3: NAR's IP Address Reserved: Set to zero. New IPv4 Address: NAR's IPv4 address or the NCoA assigned by NAR. 7.3. New Router Prefix Information Option This option is used in the PrRtAdv message. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Option-Code | Prefix-Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 11: New Router Prefix Information Option Format Fields: Type: To be assigned by IANA Length: The length of the option (including the Type, Length and Option-Code fields) in units of 8 octets. Option-Code: 0 Koodli & Perkins Expires September 1, 2007 [Page 21] Internet-Draft MIP4 Fast Handovers February 2007 Prefix-Length The number of leading bits that define the network number of the corresponding Router's IP Address option. Reserved: Set to zero. 8. Security Considerations As outlined in [rfc4068], the following vulnerabilities are identified and the solutions mentioned. Insecure FBU: Failure to protect the FBU message could result in packets meant for an address being stolen or redirected to some unsuspecting node. This concern is similar to that in Mobile Node and Home Agent relationship. Hence, the FBU and FBack messages MUST be protected using a security association shared between a mobile node and its access router. In particular, the MN - PAR Authentication Extension MUST be present in each of these messages. This document does not specify how the security association is established between a MN and the AR/FA. Secure FBU, malicious or inadvertent redirection: Even if the MN - PAR authentication extension is present in an FBU, a MN may indevertently or maliciously attempt to bind its PCoA to an unintended address on NAR's link, and cause traffic flooding to an unsuspecting node. This vulnerability is avoided by always binding the PCoA to the NAR's IP address, even when the NAR supplies an NCoA to use for the MN. It is still possible to jam NAR's buffer with redirected traffic. However, the handover state corresponding to the MN's PCoA has a finite lifetime, and can be configured to be a few multiples of the anticipated handover latency. Hence, the extent of this vulnerability is small. Communication between the access routers: The access routers communicate using HI and HAck messages in order to establish a temporary routing path for the MN undergoing handover. This message exchange needs to be secured to ensure routing updates take place as intended. Koodli & Perkins Expires September 1, 2007 [Page 22] Internet-Draft MIP4 Fast Handovers February 2007 The HI and HAck messages need to be secured using a pre-existing security association between the access routers to ensure at least message integrity and authentication, and should also include encryption. 9. IANA Considerations All the messages and the option formats specified in this document require Type assignment from IANA. Specifically, the Types, Sub- types and the Codes need assignment from ICMP, Mobile IP and Experimental Mobility Type [rfc4065] registries. 10. Acknowledgement Thanks to all those who expressed interest in having a Fast Handovers for Mobile IPv4 protocol along the lines of [rfc4068]. Thanks to Vijay Devarapalli, Keng Leung for their review and input. Kumar Viswanath and Uday Mohan implemented an early version of this protocol. Many thanks to Alex Petrescu for his thorough review that improved this document. 11. References 11.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [rfc1256] Deering, S., "ICMP Router Discovery Messages", RFC 1256, September 1991. [rfc2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [rfc3344] Perkins (Editor), C., "IP Mobility Support for IPv4", RFC 3344, August 2002. [rfc4065] Kempf, J., "Instructions for Seamoby and Experimental Mobility Protocol IANA Allocations", RFC 4065, July 2005. [rfc4068] Koodli (Editor), R., "Fast Handovers for Mobile IPv6", RFC 4068, July 2005. Koodli & Perkins Expires September 1, 2007 [Page 23] Internet-Draft MIP4 Fast Handovers February 2007 11.2. Informative References [draft-mip4-ro] Perkins, C. and D. Johnson, "Route Optimization in Mobile IP (work in progress). Internet Draft, Internet Engineering Task Force", February 2000. [ieee-802.11r] "IEEE Standard forLocal and Metropolitan Area Networks: Fast Roaming/Fast BSS Transition, the IEEE Task Group TGr. Technical report, IEEE.". [ieee-802.1x] "IEEE Standard for Local and Metropolitan Area Networks: Port-Based Network Access Control. Technical report, IEEE.". [ieee-802.21] "The IEEE 802.21 group. http://www.ieee802.org/21.". [rfc2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997. Appendix A. Change Log Addressed the following Last Call and subsequent reviews: Provided all the Code values in PrRtAdv message to cover various cases involving neighborhood discovery. Harmonized the option formats with [rfc4068]. Added the Terminology Section Added text regarding FBU message flags 'S' and 'B' Revised text in Security Considerations Clarified text in different places based on ML comments (including "forwarding", MN's use of assigned addresses in lieu of DHCP, and so on.) Clarified using ICMPv4 checksum for RtSolPr, PrRtAdv, HI and HAck Added Figures illustrating predictive and reactive handovers Koodli & Perkins Expires September 1, 2007 [Page 24] Internet-Draft MIP4 Fast Handovers February 2007 Added references to IEEE 802.21 and IEEE 802.11r All id nits (attempt to move from LaTex to xml turned out to be quite a task, sigh..) Authors' Addresses Rajeev Koodli Nokia Research Center 975 Page Mill Road, 200 Palo Alto, CA 94304 USA Email: rajeev.koodli@nokia.com Charles Perkins Nokia Research Center 975 Page Mill Road, 200 Palo Alto, CA 94304 USA Email: charles.perkins@nokia.com Koodli & Perkins Expires September 1, 2007 [Page 25] Internet-Draft MIP4 Fast Handovers February 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Koodli & Perkins Expires September 1, 2007 [Page 26]